Attempts have been made over the years to develop a lightweight electric battery for use in automobiles and other transportable applications. Of the various batteries developed to date, none offers the price/performance advantage available from the lead-acid battery (accumulator). Such a battery though, is very heavy. It uses plates made from lead which being a heavy material, adds significantly to the total weight of the battery. Lighter metals have been substituted but these could not match the price/performance ratio of the conventional lead-acid battery. Lead was found to be essential if the original storage density and charge/discharge rates were to be preserved.
The electrode of a conventional metal-acid battery are formed as plates spaced apart and immersed in an acid solution such as diluted sulfuric acid. For improved discharge characteristics, a so-called pasted plate is used which comprises a grid to which a paste containing an active mass is applied. FIG. 1 shows the structure of a grid from such a plate. The grid is made from a sheet 1 of active metal such as antimony lead in which a plurality of holes 2 are formed, defining grid elements 3 therebetween. A paste 4 comprising of an active mass such as lead oxide for example, is applied to fill the holes 2 and react with the grid elements 3. The combination of active mass and grid form the pasted plate shown in cross section in FIG. 2. In addition, the sheet 1 is provided with a terminal portion 5 for conducting electric current to and from the grid elements 3.
The grid functions as a structural frame for giving the pasted plate its shape. The outer surface 6 of each grid element 3, as indicated by the dotted lines in FIG. 2 contacts and reacts with the paste 4. Electrical current is carried by the grid between the reaction surface 8 and the terminal 5.
Conventionally, battery weight is reduced by making the grid sheet 1 as thin as possible since only the surface 6 (as indicated by the dotted lines in FIG. 2) of the grid elements reacts with the active mass 4. The grids can be made as thin as 3 mm. Further reduction was not possible because lead is a weak material. If made substantially thinner, the grid would break when the battery is subjected to vibration such as a severe jolt from the roadway or from mechanical shock due to high current charging and discharging. Even at the present thickness, batteries are not reliable when subjected to severe roadshock and they age quickly when cycled through high current charging/discharging.
Weight reduction is desirable for employment of such storage batteries (accumulators) in electric vehicles, hybrid vehicles and the like because energy efficiency is improved. Stationary applications benefit from weight reduction as well since the structural requirements of a building which houses a power back up system using storage cells such as a hospital for instance, may be reduced when the weight of the cells is reduced.